The answer is simple and it has to do with gross vs net profit.

Almost no body told us about Root barrier, which are simple digging  about 2-3 into the ground, near your foundation to cut invasive  tree roots. 

For example,Late RentInsufficient FundsUtility ReconnectionReissue CheckA/C Clean ViolationPest ControlRenewalMove-Out AdministrationUnlock RequestKey RequestFailure to Return KeyPilot LightingGrilling ViolationGarbage ViolationClogged Drain / Tub / ToiletWindow ScreenHurricane Shutter ViolationSmoking ViolationLease Amendment AmendmentPet ApplicationUnauthorized PetGuest ViolationUnauthorized OccupantInspection (due to tenant violation)Yard RemediationPool RemediationSmart Home Device TamperExterior Maintenance ViolationParking ViolationCommunity Amenity ViolationMarketing (tenant early termination)Notice (due to tenant violation) PreparationNotice DeliveryLien ViolationSubleaseAssociation ViolationEviction (not including attorney’s fees and eviction costs)Rent Verification10.

It sounds simple but lot of work is involved.

If you are referring to residential rents then you have answered your question- "Buying right"But buying right is too simple an answer. 

When I’d reach out, I would simply say something simple like “I'm looking for fixer-upper houses and can buy it off market for an on market price.

KISS - Keep it Simple...The more complex an investment does not make it better.

I asked a simple question.

Hello Mary, without knowing much more you could structure a simple partnership or hold this property in an LLC which can be divided up as you see fit.

I found that most of recommendations to buy a duplex emphasis on positive cashflow or match with simple 1% rule to start with.